Water-impermeable, gas-permeable coating compositions, method of preparation and articles coated therewith



WATER-HMPERMEABLE, GASa-PERMEABLE COAT ENG COMPOSHTKQNS, METHOD F PREPARA- TEON AND ARTIQLES COATED THEREWITH Fioyd E. Bartell, Ann Arbor, Mich.

No Drawing. Application November .10, 1951 Serial No. 255,880

22 Claims. (Cl. 260-25) This invention relates to new products which may, for example, be in the form of sheets which have the characteristic of preventing or inhibiting the passage of liquid water but readily passing moisture-vapor. This invention also concerns an aqueous product, e.g. in the form of a cream or paste, which may be used in making the aforesaid material, either in sheet form as above indicated or in the form of cubes, spheres, irregular shaped pieces, etc., depending upon the particular usage to which the product is to be put.

Without intending to limit the invention, but rather to illustrate it in a number of its important aspects, it will be described and illustrated primarily in connection with sheet material, the cream or paste used in producing the sheet material and the methods employed in making both said sheet material and the cream or paste.

As above indicated, this invention concerns sheet material which prevents the passage of liquid water but readily permits the transmission of moisture-vapor. This, as discussed more fully hereinbelow, may be accomplished by having a porous particulate material, such as silica aerogel, for example, as described in (Kistler Patent No. 2,093,454) bonded with a film-forming material to form a sheeting, a coating on fabric, or other layer of material, which will prevent the passage of liquid water but readily permit moisture-vapor to pass. According to my invention I prefer to render such an aerogel, or equivalent, hydrophobic by suitable treatment, as hereinafter illustrated, before it is combined and bonded as just indicated.

Heretofore there have been various treatments for fabrics which give them some degree of water-repellency while still permitting them to pass moisture-vapor. An example of this is the so-called Zelan treatment. The Zelan treatment, however, is simply one that treats the individual fibres of the fabric, and while it produces a F fabric having a considerable degree of Water-repellency,

it possesses but a low degree of water resistance. There have also been many other prior art treatments for fabrics or sheet materials, some of which do prevent the passage of liquid water but have one or more disadvantages such as the following: bulky or voluminous treatments, such as resins, oils, or waxes, frequently providing nothing more than temporary waterproofness; many waterproofing agents are not sufiiciently heat-resistant; and the waterproofing agent itself may be too expensive for many applications. While there has been a great deal of discussion in the prior art, of one type or another, about fabrics which merely have a water-repellent treatment i.e. a ducks backing treatment, but which will not preclude the passage of liquid water, and naturally are also water-vapor permeable, there has been no prior art, to my knowledge, of sheet material which in itself is highly water-vapor permeable and at the same time will prevent the passage of liquid water. As to some of these prior art discussions, attention is called to an article entitled Water-Vapor Permeability by John T. Steam and Albert S. Cooper, In, which appeared in the March 27, 1944, issue of American Dyestutf Reporter. This article 2,893,962 Patented July 7, 1959 discusses the phenomenon of passage of moisture-vapor through fabric coated with vinyl polymers, such as the chloride acetate copolymer and the polyvinyl butyral. It points to fabrics coated with such materials by way of contrast with the use of rubber in such coatings and the article states that with such vinyl resins, employed to produce a light coated fabric using relatively little coating material, a fabric may be produced which permits a rather large amount of moisture-vapor to be transmitted through the fabric, and the statement is made that such a treated fabric, While it transmits a certain amount of water vapor, prevents the passage of liquid water, even under hydrostatic pressure up to cm. (approximately 20 inches of water, American Association of Textile Chemists and Colorists Test). The type of product under discussion in that article, as will be seen, consists of coated fabrics and the mechanism of the moisture-vapor transfer is stated to be adsorption of moisture-vapor by the coating material as well as the fiber from one side and then evaporation thereof from the other surface. This article discusses applying the resin coatings under considerable pressure on the spreading blade to one side of the sheet of cloth, which had been given a water-repellent finish with Zelan, for example. As will be apparent, and is evident from the article, such resin coatings must be kept very thin if the ability of such a sheet to transmit moisturevapor is to be good.

It is an object of my invention to produce a sheet material which in itself is moisture-vapor permeable and prevents the passage of liquid water even though the layer providing these qualities is relatively thick. It is also an object of my invention to produce such sheet material as a continuous laminate for fibrous materials. Another object of my invention is to provide an aqueous paste or cream which can be coated to provide such a sheet. A further object is to make a dried residue from such an aqueous paste, either in film or sheet form or in other form, which has some or all of the following properties: (a) is water-repellent, (b) will prevent the passage of liquid water, while being moisture vapor permeable, (c) has a low apparent density, (d) has good resistance to heat transfer and (e) has good wear-resistance. These and other objects and advantages will be apparent from the specification as a whole, taken with the appended claims.

I have discovered the following new and original articles or products (a) a cream or paste composed of an aerogel rendered hydrophobic by treatment and an aqueous blending agent and an aqueous latex, with or without vulcanizing ingredients in the case of a rubber latex; and (b) a product or article composed of such a bonded aerogel produced by drying the above cream or paste, this product having the properties of preventing the passage of liquid water, being water-repellent, having good moisture-vapor transmission, i.e. readily permitting breathing, and having good heat insulation properties. While the idea of a coated fabric which will prevent the passage of liquid water and still permit breathing has been referred to previously (Southern Regional Laboratorys article, above), such sheeted products produced by the prior known methods, as discussed in such article, are limited in water resistance and in breathing are dependent on a combination of the fabric used and the thinness of the coating. I have discovered, however, that waterresistant, water-repellent insulating films having in their sheets any desired degree of moisture-vapor transmission can easily be made in accordance with my present invention, and that I can make sheets having moisture-vapor transmissions of much greater magnitude than can be obtained by any previously known practical method. .I can make my sheets in any desired thickness without very substantially affecting their properties of moisture-vapor lieved also to be novel and original.

ingredients in my cream or paste, any of the above properties can be varied in magnitude as desired. Although some detailed steps of my method of preparing my cream or paste may not be entirely new, the volume ratio of solid porous particles, i.e. hydrophobic aerogel particles, to particles of rubber or equivalent, as disclosed below more in detail, is of a different and greater order to the best of my knowledge than has been used before in this art, and this together with the complete method is be- For example, a cream or paste having a volume ratio of hydrophobic aerogel to rubber solids of 7 to 1 has been made by me and this cream or paste can be used to give a sheeted "material (with or without reinforcement by a textile example by applying the same as a layer to a surface to be insulated.

Briefly stated, I may accomplish my results as follows: An aerogel, namely, a highly porous gel such as disclosed in the aforesaid Kistler patent or as illustrated by the commercial product Santocel (made by Monsanto Chemical Company), of suitable particle size, is

first treated with an agent to render it hydrophobic. Organic silicon compounds and water repellent resins are useful agents for this purpose and some of my first work was with polystyrene resin followed by work on compounds of the following type: R SiCL where R is an alkyl or substituted alkyl group. In the products which I employ, x was generally 2 and R was generally a methyl group, or one R a methyl group and the other R an ethyl group. Such an organic silicon compound is 'a liquid at ordinary room temperatures and the silica aerogel may be treated with such a product in vapor form in the presence of water vapor. In this treatment water vapor was introduced into the reaction chamber containing the mass of aerogel, after which approximately by weight of the silane was added as vapor to, and thoroughly mixed with, the aerogel. The reaction proceeded exothermally at room temperature, while the mixture was agitated for about an hour. One disadvantage of the reaction was that hydrochloric acid was formed during the hydrolysis reaction, necessitating subsequent removal before the hydrophobic aerogel could be successfully used.

Subsequently it has been learned that a more desirable type of organic silane to be used in treating such particles is one such as an alkoxy chlorosilane, or especially alkoxy aminosilane, of which di-tertiary-amoxydiaminosilane and di-tertiarybutoxydiaminosilane may be mentioned as examples. These materials are particularly desirable Where the paste, formed with a hydrophobic aerogel, is coated on a textile fabric, since a compound such as (CH SiCl appears to release HCl in the finished coating. Even small amounts of HCl are very detrimental 'to the strength and life of fabrics, as will be understood.

As an example of using these materials, to a mass of hydrophilic aerogel, commercially known as Santocel, manufactured by Monsanto Chemical Company, was added approximately 8 to by weight of an amide type silane as liquid as set forth above. The aerogel and liquid silane were thoroughly mixed by continuous mixing in a tumbler, and the reaction was completed within one hour. The reaction took place at room temperature and at the end of the hour the aerogel be- This product can be used, for example, to provide an insulating layer, as for Cir 4 4 came completely hydrophobic, and the monomolecular film of water repellent surface formed on the gel structure appeared to be accomplished either by a chemical reaction or a chemi-sorption process. The hydrophobic surface of the gel structure was so permanent that vigorous and prolonged agitation or shaking with water failed to remove the film or measurably reduce the highly hydrophobic nature of the surface. In fact the resulting aerogel was so hydrophobic that it was practically impossible to wet it with water or to effect bonding with aqueous dispersions of rubber such as latex. The above as well as other methods of rendering the hydrophilic aerogel hydrophobic are described in my copending application Serial No. 78,659, filed February 26, 1949.

A hydrophobic aerogel as just described above is next incorporated in an aqueous dispersion, so as to produce a dispersion containing the hydrophobic aerogel particles, particles of latex rubber or equivalent, suitable dispersing or stabilizing agents, and water, the water being in the continuous phase in the finished dispersion or paste. This combining of materials to get the desired result may be accomplished in a plurality of ways. In my early work I accomplish this by mixing the hydrophobic aerogel directly with natural rubber latex containing an agent, e.g. methyl cellulose, for dispersing the hydrophobic aerogel. The procedure I employed was as follows: 400 cc. of hydrophobic silica aerogel (approx. 40 g. of 0.1 sp. gr. aerogel) was placed in a cylindrical vessel approximately six inches in diameter and slowly stirred while 300 cc. of solution of a mixture of cc. of natural rubber latex (28%) and 150 cc. of methyl cellulose (2% aq. soln.) was slowly added. The stirring was effected by using a standard mechanical stirrer or mixer having offset and staggered rubber blades approximately two inches wide, the blades being so positioned as to rub against the side walls of the vessel during rotation; the flexible blades acted not only to stir and mix the hydrophobic powder with the aqueous latex phase but also set up a shearing and rubbing action which was conducive to the production of a smooth paste. After a preliminary stirring at a speed of approximately 200 r.p.m. for a period of two minutes, the liquid became uniformly distributed throughout the aerogel powder so that at this point it appeared perfectly dry. (This intermediate product is also considered novel and in some cases it may be desirable to ship the product to the user in this form, continuing the mixing later.) The speed of the stirrer was next increased to about 600 r.p.m. so as to assert a definite shearing force within the mass and provide a vigorous rubbing against the walls of the vessel. By this action the liquid droplets in the mass were gradually pulled out and elongated so that the surface areas were greatly extended to form fluid films. As the stirring progressed, these films of rubber latex and blending agent apparently gradually and partially enveloped particles of the aerogel powder and within about one minute from the time speed was increased the entire mass became relatively fiuid. The same process was repeated on another sample of the same materials except that a concentration of ammonia that gave a pH of approximately 10 was added to the mix. This gave a smooth, easily workable paste.

Later I found that I could also get a satisfactory paste by mixing the hydrophobic aerogol directly into water containing a suitable blending or dispersion agent therefor. For example by mixing 7 parts of aerogel by weight into 16 parts by weight of a 2% aqueous methyl cellulose solution, to which is immediately added 16 additional parts of water, and by subjecting this to a mixing action. e.g. in a mixer as above discussed, revolving the stirrer at a rate to provide a peripheral speed approximately equivalent to that obtained at 1100 r.p.m. on a 10 inch diameter container, the water first seems to disappear in the relatively large volume of aerogel and the batch becomes quite dry appearing. However upon continued mixing at the same rate the batch first begins to take on something of the characteristics of wet saw dust and then,

quite suddenly, becomes quite fluid and acquires approximately the consistency of whipping cream. What is believed to happen is that in the early stages of the mixing the water solution of methyl cellulose accumulates as small discrete droplets over the surface of the aerogel particles within the batch, and then, with further mixing, the droplets of the water solution gradually coalesce, and become the continuous phase, so that the material resulting at the end of the mixing (which is of approximately the consistency of whipping cream) is a dispersion of the hydrophobic aerogel in the aqueous methyl cellulose solution. The entire time of mixing may be about 2 minutes. This aqueous product (of the consistency of whipping cream) may then be easily and readily mixed with a natural latex milk, or with any other suitable latex, to form my finished paste or cream. For example, 24 parts of a 60% natural latex may now be added to the product just produced and then be very easily mixed therewith by any suitable, simple mixing operation. Additionally suitable vulcanizing agents, e.g. in dispersion form, may be added with the latex. For example, 1.2 to 2.4 parts of a vulcanizing agent such as Vanderbilt G3, which is a mixture of zinc oxide, sulfur, para benzyloxyphenol, zinc dibutyldithiocarbonate, sodium salt of alkyl naphthalene sulfonic acid, casein, caustic soda and water, may be added to the 24 parts of 60% natural latex before the latter is added to the hydrophobic cream above discussed. The vulcanizing agent just mentioned is a mixture of several ingredients well known in the art of vulcanizing rubber. Any suitable rubber or equivalent employed, where vulcanization is desired. The finished cream or paste has a consistency approximately intermediate that of milk and whipping cream, though it may obviously be varied in consistency within a substantial range, depending upon the use to which it is to be put.

Instead of having the entire volume of hydrophobic aerogel present in the aqueous methyl cellulose solution at the beginning of the mixing, as in the operation just described above, it may be added in increments to the methyl cellulose solution. For example, 1 part by Weight of the hydrophobic aerogel may be added to the 32 parts of 1% methyl cellulose solution and then the additional 6 parts may be added in 6 equal increments, for example, an additional increment being added after the previous increment has been incorporated in and dispersed in the aqueous solution.

The finished paste as above described, however produced, may next be used in making any desired sheet material, having characteristics as above indicated. For example, the hydrophobic cream or paste last discussed may, without further change, be coated directly between two layers of cloth. As an example, the cloth may be 3 oz. cotton balloon cloth (3 ounces per running yard, 39 wide). The paste is coated on one of said sheets and then may be passed through a knife coater, another sheet of the same cloth being brought into contact with the exposed surface of the paste just before it passes through the knife center. The resulting product coming from two sheets of cloth with a sandwich of the hydrophobic paste therebetween. Upon drying to eliminate the water, as by passing through a tunnel dryer, being held in shape during drying by tenter frame arrangement, the resulting product will readily transmit moisture-vapor, will prevent the passage of liquid water, and has good insulating qualities, making it useful for example, in the making of sleeping bags and many other articles. The knife coater may be set, in making such product, so that the finished sheet has an over-all thickness of approximately .015 to .035 inch, more or less, as desired.

A sheet material as just described may, where desired, have the exposed surfaces of the two sheets of cloth treated to render them water-repellent, as by a Zelan treatment, so as to minimize the tendency of the finished sheet to absorb water and become heavy, a factor which is of special importance in connection with sportsmenh jackets, hunting pants, searneris coats and the like.

A further example The same type and amount of hydrophobic silica aerogel was used, as described previously (column 3), and with this was mixed a cc. of neoprene synthetic latex (approximately 15% neoprene rubber content), 100 cc. of natural rubber latex (approximately 28% rubber), and cc. of a 2% methyl cellulose aqueous solution. These compounds were mixed and stirred as above described. The paste thus produced was formed into a sheet as above described and, when dried, the product possessed excellent bond and was tough and flexible. In subsequent tests it was found that a sheet product was obtained with the use of synthetic latex alone, instead of the above combination of synthetic and natural latices.

A third example The same type and amount of hydrophobic silica aerogel was used as described above and with this was used 100 cc. of natural rubber latex (approximately 28% rubber), together with 300 cc. of a 2% aqueous solution of polyvinyl alcohol (grade RH-49l). After mixing and stirring as described in connection with the above example, a smooth workable paste was obtained which was formed into a sheet as above described and then dried, resulting in a well bonded, tough and flexible sheeted product.

A fourth example in this example diatomaceous earth was substituted for the hydrophilic aerogel used in the preceding examples and an amide type silane, e.g. (C H O) Si(Nl-I in an amount approximating 6 to 12% of the weight of the diatomaceous earth, was added thereto. The liquid silane was added to the diatomaceous earth in small increments over a period of approximately 5 minutes instead of adding the silane as a liquid to the mass all at one time, as was done in the treatment of the aerogel as above described. Otherwise the steps were carried out as illustrated above in connection with the silica aerogel and the resulting product was quite comparable to the hydrophobic silica aerogel as above described except that it had a somewhat higher specific gravity.

400 cc. of the hydrophobic diamotaceous earth was then mixed with 100 cc. of natural rubber latex (20% rubber) and 3G0 cc. of an approximately 2% solution of polyvinyl alcohol (grade RBI-491) in water. This compound was mixed and stirred in the manner above described until a workable paste was obtained. This paste was then formed into a sheet and dried to form a coherent bonded hydrophobic diatomaceous earth, which sheet or slab possessed excellent bond and was tough and flexible.

While the detailed example first given above described a finished sheet material, involving two sheets of cloth having a sandwich layer of hydrophobic aerogel therebetween, I have also produced sheet material in which only one sheet of cloth was employed, one surface of the bonded aerogel, or equivalent, being exposed in this case. The other surface of the cloth, as above indicated, may also in this case be given a treatment, e.g. a Zelan treatment, or other treatment to render the exposed surface of the cloth water-repellent, or to give it other suitable characteristics.

It has also been found that my aerogel cream or paste, or equivalent, may be coated on both sides of a sheet of cloth, paper or the like, likewise providing a sheet which will readily permit moisture-vapor to pass but will prevent the passage of liquid water.

My cream or paste may also be formed into a sheet without any additional support, although any suitable support may be used as a manufacturing expedient, for example, a sheet or web of paper.

Somewhat altered characteristics may be given to my bonded aerogel or equivalent, in dried form, depending upon the properties desired, as for example by introducing any desired amount of glass fibres, resin fibres, asbestos fibres, paper fibres, or of any suitable triturated material. Such additives may also have advantages where the finished bonded aerogel or equivalent is in form other than sheet form, as hereinabove illustrated, depending upon the particular properties desired.

My cream or paste may be coated on surfaces to be insulated, as for example on metal or enameled panels forming the side walls of refrigerators, such as ordinary household refrigerators. In this case, however, it is generally desirable to increase the ratio of the aerogel to the rubber substantially beyond the ratio usually employed in forming sheeted material. For example, I have found that I can produce ratios of aerogel to latex solids as high as 35 to l and still have a cream or paste which can be bonded to refrigerator elements and will provide a good insulation coating. Where desired, a priming coat may first be put upon the metal panel, enameled wall, or the like, to which my cream or paste will anchor itself still better. My paste may be sprayed on, troweled on, or otherwise applied to a surface to be insulated, depending upon its consistency, the thickness of layer desired, and the like. Also, where desired, 1 may apply a finishing coating over a thick layer of such insulation, the finishing coating, for example, being a thin layer of a paste which is similar except that it has a lower ratio of aerogel to latex solids. Such paste can also be used as cementing material for sheets of preformed laminate materials or for sheets of other materials.

It will be seen from the above examples, and I have determined by repeated tests, that the hydrophilic material, which is treated, may be an inorganic colloidal material in the form of the fluffy, freely flowing cellular aerogel, such as Santocel, as well as diatomaceous earth, or equivalent materials, and it will be understood in the specification and claims that wherever the words silica aeroge is used, it refers to a light weight porous material which originally was in the nature of the hydrophilic aerogels set forth in the above mentioned Kistler patent, or to diatomaceous earth. It will also be understood that other ways of rendering the aerogel or equivalent material hydrophobic may readily occur to those skilled in the art.

When natural rubber latex is used as the bonding agent antioxidant agents should be incorporated into the formula; about 1% antioxidant in respect to the latex is satisfactory. Phenyl-beta-naphthylamine, aldol-alphanaphthylamine or similar antioxidants may be use Vulcanizing agents and accelerators may also be used to alter the properties of the latex and vary the stability of the bonded product. It also will be understood that any of the well known aqueous dispersions of resins may be substituted for natural or synthetic latex and accordingly the word latex in the specification and claims contemplates the various known aqueous dispersions or emulsions of finely divided rubber or resin particles having rubber-like properties whether natural or artificial; for instance, the synthetic latices may include butadiene, Vistanex, which is a high molecular weight polymer of isobutylene identified by the formula (ho-C li vinyl compounds, etc.

It will also be understood that blending agents other than methyl cellulose and polyvinyl alcohol may be used in forming the bonded hydrophobic aerogel, one example being a solution of zinc aerosol, a zinc sulfosuccinic acid ester salt, chemically known as zinc bis(2-ethylhexyl) sulfosuccinate, of approximately 2% concentration. However methyl cellulose and polyvinyl alcohol are much preferred. A preferred methyl cellulose is one which, in water, gives a high viscosity, preferably the one known as the 1500 centipoise methyl cellulose. Other dispersing agents such as sodium oleate, starch and sodium lauryl sulfate may be used but these do not produce the smooth, homogeneous paste obtained through the use of methyl cellulose, zinc aerosol," and polyvinyl alcohol.

An important feature of the present invention is that a thin bonded sheet or slab formed from hydrophobic material and latex is relatively light in weight, rela tively tough and flexible, highly water repellent and buoyant, and will prevent the passage of liquid water but will nevertheless permit transfer of moisture vapor through it. The water repellency and moisture vapor permeability are attributable primarily to the hydrophobic aerogel particles and the manner in which they are held together in the bonded mass. The latex is in the form of small discrete, discontinuous particles which merely serve to bond the aerogel particles together, thus leaving a multiplicity of fine pores between the aerogehparticles. The hydrophobic aerogel particles have substantially the same porous and fibular gel structure as the hydrophilic aerogel except that in the case of the hydrophobic particles the internal and external surfaces of the gel structure are provided with a molecular film of water repellent material. The extreme water repellency of this film in combination with the fibular gel structure and the fine pores between the aerogel particles account for the water repellency and the moisture vapor permeability of the bonded hydrophobic aerogel.

When my hydrophobic bonded paste, such as is set forth in any of the above examples, is applied to solid surfaces such as metal, wood or fabric, it exhibits sufficient adhesion so that, when dried, it maintains itself firmly in position under ordinary conditions of use. This property of the bonded paste makes possible easy application of the paste to most any type of surface. For example, fabrics may be prepared by coating one side, or both sides, with the bonded paste or, by using the bonded paste between two pieces of fabric, it is possible to prepare a laminated fabric having unusual properties. Fabric so treated and dried will be very light in weight, as a bonded material of only a few hundredths or even a few thousandths of an inch in thickness will give a water repellent, rain proof fabric which can be worn in comfort, since it will permit the escape of water vapor outward through it from the wearer, and unlike rubberized waterproofed fabric it will not cause the Water vapor to condense inside. Laminated fabric clothing, as a raincoat, containing a layer of my hydrophobic bonded material of less than 0.03 inch in thickness will withstand a hydrostatic head of more than five feet of water and will at the same time give sufficient water vapor permeability to permit passage of vapor of all water excreted as perspiration from a person subjected to fairly vigorous exercise. Tests have shown that body perspiration, upon vigorous exercise, amounts to approximately 15 to 20 gms./hr./sq. m. of body surface. My sheet material will readily transmit this much moisture vapor, and tests have further shown that I can readily produce sheets in accordance with my present invention which will transmit moisture vapor at a rate up to 40- 50, or more, gms./hr./sq. m., while still maintaining good resistance to the passage of liquid water. No prior practical sheet structures have ever been devised, to the best of my knowledge, which will simulate or at all approach these conditions.

Clothing that is both warm and water repellent can be prepared by using relatively thicker bonded layers within the laminated fabric. The thermal insulation of the main constituent of the bonded material is better than that of any known available insulating material. Tests have shown typical samples of the bonded aerogel to possess a thermal conductivity of not greater than 20 10 cal.

cm. sec. C. cm.

Laminated bonded material, preferably a relatively thick layer approximately ca be used in the construction of footwear, mittens, sleeping bags, blankets, etc.

Fabrics coated or laminated with my hydrophobic bonded material can be made with equipment usually found in textile coating and finishing plants. Single coatings in relatively thick or thin layers can be applied with a knife spreader. After partial or even complete drying of such coatings, successive coats may be applied if desired. Suitable lamination can be made by passing the fabric, with paste between the layers of fabric, through a set of positioned squeeze rolls. The sheet thus formed can be passed directly into a standard textile dryer. If the sheets are thin they can be dried by passing them over standard can driers. If they are relatively thick they can be dried by passing them slowly through a tenter frame drier. The drying of the laminated material offers no serious difficulties as sheets as much as A" thick will dry within an interval of a few hours even when allowed to stand at ordinary room temperature, since the hydrophobic nature of the incorporated solid or semi-solid material tends to drive the water out of the aqueous bonding phase rather than to retain it within the paste structure. The flexible laminated fabric can readily be cut with ordinary shears and can be made into garments by the usual processes of sewing or cementing the seams.

The hydrophobic bonded material can be used for insulation purposes in many different ways. The hydrophobic bonded paste can be formed into blocks or sheets which when dry can be used where needed; or the paste can be laminated between fabric, wood, or metal and the like; or the paste can be poured into spaces to be insulated and allowed to dry and set; or the paste can be sprayed or troweled upon the surface it is desired to insulate. The latter method would be especially desirable in the insulation of irregular shaped surfaces containing crevices such as might exist on the interior surface of aeroplanes, automobiles and the like.

A further feature of my invention is the use of the hydrophobic bonded paste for buoyancy purposes as for example in flotation devices, in life preservers and related equipment. By making use of bonded hydrophobic silica aerogel or other low specific gravity hydrophobic solid or semi-solid, paste can be prepared which can be extruded in almost any form as in ropes, rods, etc. The ropes when dry are of exceedingly low specific gravity and can be cut into any desired lengths. Such pieces can readily be attached to apparatus or to clothing or can be inserted into prepared pockets of desired shapes or sizes, thus affording a means of flotation in water. Since the bonded hydrophobic aerogel is extremely water-resistant and water-repellent it will retain its flotation characteristics quite indefinitely. In this respect it is far superior to products now in use for life preservers such as for example kapok and the like.

Another important feature of this invention, lies in the fact that coloring materials, dyestuffs and even water soluble dyes such as methylene blue can be added to the original formulas used in making the paste. The coloring material is adsorbed. The dry bonded material is uniformly colored and the color is resistant to removal by water. This is because of the highly water repellent nature of the bonded mass. Thus colored, the bonded material can serve as a decorative material on the surface upon which it is applied.

It should be pointed out also that the bonded hydrophobic material has good electrical insulation properties and that it can be used to advantage where ease of application, lightness in weight, and a high degree of water repellency are of importance in relation to the electrical insulation.

The principal properties of my new product are high water repellency, high water resistance, water vapor permeability, high thermal insulation, low specific gravity and good electrical insulation. All of these characteristics can be obtained in a single product but all may not be needed in any given product. For example, depending on the hydrophobic solid used, it is possible to obtain either a high density (sp. gr.) or low density product in which all other characteristic properties could be retained. This feature would be of importance in relation to buoyancy.

While I have illustrated my invention in various details, this has been by way of description and not by way of limitation. Salient features of my invention involve my paste or cream, above described, comprising aerogel as aforesaid dispersed in a latex, and also the dried residue of such cream or paste, either in the form of coatings or sheets or in other desired form, with or without other ingredients. However all embodiments within the scope of this application and/or of the appended claims are comprehended.

This application is a continuation-in-part of my earlier application Serial No. 160,580, filed May 6, 1950, which earlier application was in turn a continuation of application Serial No. 696,956, filed September 13, 1946, now abandoned.

I claim:

1. A flexible continuous film or sheet comprising compounded synthetic material which readily transmits moisture vapor but prevents the passage of liquid water and which includes silica aerogel particles the entire fibular structure of which is hydrophobic, said hydrophobic aerogel particles possessing substantially the same porous gel structure and surface structure as hydrophilic aerogel particles and being bonded together with the solid constituent of a latex having rubber-like properties, said aerogel being incorporated in said material in a greater volume proportion than the solid latex constituent.

2. A film or sheet comprising compounded synthetic material which readily transmits moisture vapor but prevents the passage of liquid water and which includes particles of silica aerogel having a Water repellent monomolecular film on the gel structure thereof, said hydrophobic aerogel particles possessing substantially the same porous gel structure and surface structure as hydrophilic aerogel particles and being bonded together with small, discontinuous particles of the solid constituent of a latex having rubber-like properties to form a bonded continuous mass possessing porosity, toughness and flexi bility, said mass being comprised essentially of said silica aerogel.

3. A fibrous sheet having on at least one surface there of a tough, flexible coating of compounded synthetic material which readily transmits moisture vapor but prevents the passage of liquid water under a substantial hydrostatic head, said coating including silica aerogel particles the entire fibular structure of which is hydrophobic, said hydrophobic aerogel particles possessing substantially the same porous gel structure and surface structure as hydrophilic aerogel particles and being bonded together with the solid constituent of a latex having rubber-like properties, the latex being incorporated with said aerogel in an amount such that said coating is comprised essentially of aerogel.

4. An aqueous cream or paste comprised of silica aerogel particles substantially uniformly mixed with a rubber-like latex, the entire fibular structure of said aerogel particles being hydrophobic, said hydrophobic aerogel particles possessing substantially the same porous gel and surface structure as hydrophilic aerogel, said latex being the continuous phase of said paste.

5. An article of manufacture comprising silica aerogel particles rendered hydrophobic by a Water repellent monomolecular film on the entire internal and exposed fibular structure thereof and bonded together with small, discontinuous particles of the solid constituent of a latex having rubber-like properties in a tough and flexible mass, said aerogel and latex being combined in a volume ratio of four and one half to thirty-five parts of aerogel to one part of solids deposited from said latex.

6. A workable paste comprising hydrophobic silica aerogel, the discrete particles of which are hydrophobic throughout the gel structure thereof and possess the fibrous surface and porous structure of hydrophilic aerogel, and a rubber-like latex substantially uniformly mixed, said aerogel and latex being combined in said paste in a volume ratio of at least seven parts of aerogel to one part of latex solids, said latex forming the continuous phase of said paste, said paste when dry forming a continuous, flexible solid mass.

7. A compounded synthetic film or sheet material including silica aerogel, the discrete particles of which are hydrophobic throughout the gel structure thereof and retain the fibrous surface and porous structure of hydrophilic aerogel, and the solid constituent of a latex having rubber-like properties, said material having a moisture vapor transmission of at least 15 gms./hr./sq. m. and which prevents the passage of liquid water therethrough under a hydrostatic head of greater than 20 inches.

8. A flexible continuous film or sheet comprising compounded rubber like synthetic material which includes finely divided silica aerogel bonded together by latex to form a sheet providing a high degree of Water repellency and water resistance, said material containing a multiplicity of fine pores so as to permit the ready passage of moisture vapor.

9. A porous fibrous material having a rubber like coating of a finely divided bonded material, said coating comprising hydrophilic silica aerogel particles rendered hydrophobic by a film of hydrophobic material on the surfaces of the gel structure, said particles being held together by latex and providing a high degree of water repellency and water resistance and containing a multiplicity of fine pores so as to permit the ready passage of moisture vapor.

10. Those steps in the forming of a paste workable into sheet form and adapted to form upon drying, a highly water resistant, vapor permeable mass which comprises treating a relatively large quantity of silica aerogel, the discrete particles of which have been rendered hydrophobic throughout the fibular structure thereof and retain the generally porous surface and fibular structure of hydrophilic aerogel, with a water-soluble dispersing agent selected from the group consisting of: methyl cellulose,

polyvinyl alcohol and zinc bis(2-ethylhexyl)sulfosuccinate, to render the aerogel dispersible in water and mixing the aerogel with a lesser amount of a rubber-like latex.

11. Those steps in the forming of a water repellent, vapor permeable coating material with silica aerogel which comprises treating the entire internal and exposed fibular structure of the gel with a relatively fluid hydrophobic film forming material to form on the surfaces of the gel structure a water repellent monomolecular film and mixing the aerogel with a rubber-like latex to form a workable paste which may be applied to porous surfaces as a thin coating, said latex being mixed with the aerogel in an amount such that said paste is comprised essentially of aerogel.

12. Those steps in the forming of a water repellent, vapor permeable coating material with hydrophilic silica aerogel which comprises bringing the internal and exposed surfaces of the gel structure into contact with a relatively fluid organic silane compound to form on said surfaces of the gel a water repellent monomolecular film without destroying the generally porous and fibular structure of the hydrophilic aerogel, treating the aerogel with a dispersing agent selected from the group consisting of: methyl cellulose, polyvinyl alcohol and zinc bis(2-ethylhexyl)sulfosuccinate, and mixing the aerogel with a rubber-like latex in a volume ratio of at least seven parts of the aerogel to one part of latex solids.

13. Those steps in the forming of a water repellent, vapor permeable coating material with silica aerogel which 12 comprises bringing the internal and exposed surfaces of the gel structure into contact with a relatively fluid organic silane compound, treating the aerogel with a dispersing agent selected from the group consisting of: methyl cellulose, polyvinyl alcohol and zinc bis(2-ethylhexyl)sulfosuccinate, and mixing the aerogel with a rubber-like latex.

14. Those steps in the forming of a Water repellent, vapor permeable coating material with silica aerogel which comprises bringing the internal and exposed surfaces of the gel structure into contact with an alkoxyaminosilane in a relatively fluid state, treating the aerogel with a dispersing agent selected from the group consisting of: methyl cellulose, polyvinyl alcohol and zinc bis- (Z-ethylhexyl)sulfosuccinate, and mixing the aerogel with a rubber-like latex in a volume ratio of at least seven parts of aerogel to one part of latex solids.

15. Those steps in the forming of a water repellent, vapor permeable coating material with silica aerogel which comprises bringing the internal and exposed surfaces of the gel structure into contact with an alkoxyaminosilane in a relatively fluid state, treating the aerogel with a dispersing agent selected from the group consisting of: methyl cellulose, polyvinyl alcohol and Zinc bis- (2-ethylhexyl)sulfosuccinate, and mixing the aerogel with a rubber-like latex.

16. The product made in accordance with the method defined in claim 11.

17. A garment having a portion thereof comprising a synthetic film material, said material being itself impervious to the passage of liquid water therethrough and containing a multiplicity of fine pores which permit the ready passage of moisture vapor therethrough, said material including silica aerogel the entire internal and exposed fibular structure of which is hydrophobic, said hydrophobic aerogel particles possessing substantially the same internal and external fibular and generally porous structure as hydrophilic aerogel, and latex having a solid constituent possessing rubber-like properties.

18. A garment having a portion thereof comprising a synthetic film material which in itself has a moisture vapor transmission of at least 10 gms./hr./sq. m. and which in itself prevents the passage of liquid water therethrough under a hydrostatic head of at least 20 inches, said film material including particles of hydrophobic silica aerogel bonded together in a latex matrix the solid constituent of which has rubber-like properties.

19. A water-impervious and water vapor-permeable fabric which comprises a textile fabric coated with a continuous layer of rubberlike material, said material containing silica aerogel and latex, said aerogel and latex being combined in the volume ratio of four and one-half parts of aerogel to one part of latex.

20. The method of preparing a water-impervious water vapor-permeable coated fabric which comprises mixing a latex of a rubberlike self-polymer with from four and one-half to thirty five volumes, based on the polymer, of silica aerogel, and applying a continuous layer of said polymer on a textile fabric by spreading the mixture on the fabric, and drying the coating by evaporation of the water in the latex to form a multiplicity of fine pores.

21. The product made in accordance with the method defined in claim 13.

22. A flexible continuous film or sheet comprising compounded synthetic material which readily transmits moisture vapor but prevents the passage of liquid water and which includes silica aerogel particles the entire fibular structure of which is hydrophobic, said hydrophobic aerogel particles possessing substantially the same porous gel structure and surface structure as hydrophilic aerogel particles and being bonded together with the solid constituent of natural rubber latex, said aerogel being incorporated in said material in a greater volume proportion than the solid latex constituent.

(References on following page) References ited in the file of this patent UNITED STATES PATENTS Klein et a1 Apr. 9, 1929 Crawford et a1. Apr. 25, 1933 5 Beckwith Dec. 24, 1935 Bodollet May 19, 1936 14 Alton et a1. Apr. 26, 1938 Omansky Ian. 6, 1942 Rand Apr. 2, 1946 Safiord July 29, 1947 Bass Oct. 7, 1947 Beauchamp Nov. 20, 1951 Kistler Mar. 18, 1952 

1. AN FLEXIBLE CONTINUOUS FILM OR SHEET COMPRISING COMPOUNDED SYNTHETIC MATERIAL WHICH READILY TRANSMITS MOISTURE VAPOR BUT PREVENTS THE PASSAGE OF LIQUID WATER AND WHICH INCLUDES SILICA AEROGEL PARTICLES THE ENTIRE FIBULAR STRUCTURE OF WHICH IS HYDROPHOBIC, SAID HYDROPHOBIC AEROGEL PARTICLES POSSESSING SUBSTANTIALLY THE SAME POROUS GEL STRUCTURE AND SURFACE STRUCTURE AS HYDROPHILIC AEROGEL PARTICLES AND BEING BONDED TOGETHER WITH THE SOLID CONSTITUENT OF A LATEX HAVING RUBBER-LIKE PROPERTIES, SAID AEROGEL BEING INCORPORATED IN SAID MATERIAL IN A GREATER VOLUME PROPORTION THAN THE SOLID LATEX CONSTITUENT. 